In Australia our A bodies use the US floorpan with offset driveline to our R/H drive. This makes for a very tight R/H side near the steering box so much t hat we run a remote oil filter set up from the factory as the standard filter placement would go through the steering box. One of our mopar experts decided to develop a high HP header system and experimented with many designs over a few years. In his words he expected 4 into one was the ultimate for power but it is very hard in our limited space. he designed and built a development of our already try why design and it made more power than the 4 into ones. The old ones are 1 5/8 x 1 3/4 x 2 1/2 and the new design is 1 3/4 x 2 x 3 inch.I had the old system on my 410 and made 355 rwhp . the new system made 392 rwhp. A increase of 37 rwhp. I have changed the heads to trick flows from the edelbrocks and now make 425 rwhp.